Various attempts in the past have been directed toward the monitoring of telephone calls either to determine the elapsed time or to automatically calculate charges incurred by the telephone call or the number of call units consumed during use of the telephone. An example of such a device is disclosed in U.S. Pat. No. 3,508,392 to Temps wherein two electric switches are mounted adjacent a typical wall-mounted telephone and which control the operation of an electric clock. The clock is started by means of a switch mounted next to the telephone dial so that when the dial is turned the switch actuates a relay thereby starting the clock. Replacement of the telephone receiver in its cradle deactivates the clock by means of a second switch externally connected to the receiver bracket.
Another patent, U.S. Pat. No. 3,769,463 to Graham et al, discloses a system wherein the accumulative cost of a given telephone call is calculated by an electronic claculator after the user programs the device with the necessary rate information.
Similarly, U.S. Pat. No. 3,555,193 to Brand, U.S. Pat. No. 3,962,548 to Stone and U.S. Pat. No. 3,970,793 to Profitt et al disclose devices for timing and charging of long distance telephone calls wherein manual operations either set rate information or start the device with digital rate information being calculated by the machine upon termination of the telephone call. This digital information is provided by a series of discs, and in the case of the Profitt et al disclosure, a digital timer is provided.
Generally, such devices have operated with some degree of success when used with a single line, such as in the Temps patent, or when the proper cost data is manually inserted into the device or provided by the operator. However, there is a need for a system which is capable of accumulating elapsed time of use for each of a given plurality of telephone access lines, such as for instance in recording the usage of WATS lines into different regions or geographical areas.